Nutrient chemistry of the Ob' and Yenisey Rivers, Siberia: results from June 2000 expedition and evaluation of long-term data sets

Abstract

Abstract Although containing only ∼1% of global ocean volume, the arctic Ocean receives almost 10% of global river discharge. Nutrients carried by arctic rivers influence the productivity of their estuaries and coastal seas and may serve as important indicators of changing conditions in their watersheds. The three largest arctic rivers (Yenisey, Ob', and Lena) enter the arctic Ocean from Siberia and together account for nearly 35% of river-water inputs to the arctic Ocean. Although several nutrient flux estimates have been published for Eurasian arctic rivers, recent publications have highlighted uncertainties in these estimates and have cautioned against their uncritical use, particularly with respect to ammonium data. In order to help clarify the situation and evaluate the validity of existing long-term data sets, we went to Siberia during June 2000 to collect and analyze new nutrient samples from the downstream reaches of the Yenisey and Ob' rivers. Samples were independently analyzed by as many as four groups/laboratories in order to maximize confidence in analytical results. Whereas long-term data sets report average ammonium concentrations of 710 and 360 μg N/l in the Ob' and Yenisey rivers, respectively, we measured concentrations of only 10–15 μg N/l in both rivers in June 2000. We conclude that existing long-term data sets for these two rivers are grossly in error with respect to ammonium concentrations, and by extension that other surprisingly high values of ammonium reported for Russian arctic rivers (for example Pur, Taz, Nadym, and Pechora rivers) must be considered extremely doubtful. The situation is better for nitrate and phosphate, but our one-time sampling is insufficient to fully evaluate the reliability of existing data sets for these nutrients. Because a substantial percentage of the total freshwater input to the arctic Ocean comes from Russian rivers, the large revisions in ammonium concentrations needed for the Ob', Yenisey, and probably other Eurasian arctic rivers will significantly reduce estimates of dissolved inorganic nitrogen (DIN) fluxes to the arctic Ocean as a whole.